1. Field of the Invention
This invention relates to a semiconductor light-emitting device which is designed to enable a phosphor to emit light by irradiation with excitation light from a semiconductor light-emitting element and, in particular, to a semiconductor light-emitting device which employs a high-output semiconductor light-emitting element.
2. Description of the Related Art
In recent years, many attentions have been paid to a solid-state white light source consisting of a small semiconductor light-emitting device which is capable of emitting white light and includes a semiconductor light-emitting element employing a GaN type III-Group nitride semiconductor and enabled to emit near ultraviolet ray, bluish violet ray, blue ray, etc., is used as an excitation light source and part or all of the excitation light is converted into a light having a different wavelength by irradiation with the excitation light to a phosphor so as to emit white light. Since the solid-state white light source employing a semiconductor light-emitting element as an excitation light source as described above has characteristics such as low power consumption and long life, the solid-state white light source is utilized in various fields such as general lighting, on-vehicle lighting, a back light source for liquid crystal, etc.
In the case of the solid-state white light source using a combination of the aforementioned semiconductor light-emitting element and a phosphor, there is an increasing trend to adopt generally inexpensive light-emitting diodes (LED) for use as a semiconductor light-emitting element to be employed as an excitation light source (for example, JP-A 2003-142737). However, if it is tried to obtain the same or higher degree of luminescence as that of general lighting such as a fluorescent lamp or an incandescent lamp by making use of the existing LED-excited white light source, it is required to employ a plural number of LED-excited white light sources. Under the circumstances, various researches for improving the characteristics of solid-state white light source are now being studied, such researches including the development of a large area LED for the purpose of enhancing the output per chip, the improvement of light-emitting efficiency and output, the miniaturization of module size, the improvement of color rendering, the abatement of color shading, etc. (for example, JP-A 2004-119634).
Meanwhile, in view of increasing the light-emitting output, it is conceivable to employ, as an excitation light source for the solid-state white light source, not the LED but a laser diode (LD). Since this LD is higher in output and also higher in conversion efficiency on injecting high electric current as compared with the LED, it is expected to realize a small and high output solid-state white light source.
However, when this high output semiconductor light-emitting element is employed as an excitation light source, it may give rise to the problems that the properties of the semiconductor light-emitting element and of the phosphor may be deteriorated due to the influence of heat generation on operating the semiconductor light-emitting device. As a matter of fact, it is now studied to develop a structure wherein the heat releasing property is taken into account when employing a high output semiconductor light-emitting element though an LED is employed as the high output semiconductor light-emitting element in this case (see JP 2927279).
However, as described above, since LEDs which are designed to be driven with low electric current are mainly employed as an excitation light source in the case of the ordinary solid-state white light-emitting device, there are almost no studies reported so far on the influence of heat generation when using an high output semiconductor light-emitting element, especially an LD to be driven with a large driving current.